module Rack
  # Ensures only 1 thread passes through the stack the first time (subsequent requests are allowed through concurrently).
  # This is needed to work-around the thread-safety issue in http_router gem used by Padrino which results in a
  # DoubleCompileError when concurrent requests occur on server startup.
  #
  class SerialInitializer
    @@mutex = Mutex.new
    @@initialized = false

    def initialize(app)
      logger.info "SerialInitializer: #{Thread.current} created"
      @app = app
    end

    def call(env)
      if !@@initialized
        logger.info "SerialInitializer: #{Thread.current} not initialized, attempting lock"
        @@mutex.synchronize do
          logger.info "SerialInitializer: #{Thread.current} acquired lock!"
          if !@@initialized
            begin
              logger.info "SerialInitializer: #{Thread.current} within lock, app not initialized, going ahead with call"
              res = @app.call(env)
              @@initialized = true
              logger.info "SerialInitializer: #{Thread.current} app initialized successfully - this should only happen once!"
              return res
            rescue Exception => e
              logger.error "SerialInitializer: #{Thread.current} error initializing app, logging and re-raising (subsequent threads will re-attempt initialization): #{e.class} #{e.message} \n #{e.backtrace.join("\n")}"
              raise
            end
          else
            logger.info "SerialInitializer: #{Thread.current} acquired lock, but app was already initialized, calling it"
            return @app.call(env)
          end
        end
      else
        return @app.call(env)
      end
    end
  end
end